The present invention relates generally to gas turbine engines, and, more specifically, to noise suppression and infrared signature reduction therein.
In an exemplary turbofan gas turbine engine configured for powering an aircraft in flight, a fan is driven by a core engine for pressurizing ambient air to produce propulsion thrust. Combustion gases are also discharged from the core engine and contribute to propulsion thrust.
Both the fan air exhaust and the core engine exhaust are discharged at considerable exhaust jet velocities which generate noise during operation.
Various forms of jet noise suppression devices have been developed through the many decades of turbine engine use. Exhaust noise is typically reduced by reducing the maximum velocity of the exhaust streams by forced mixing with lower velocity exhaust streams. And, infrared (IR) signature is likewise reduced as the accelerated mixing process decreases the plume thermal volume.
A typical mixer is in the form of circumferentially serpentine lobes or chutes which direct fan exhaust radially inwardly and core exhaust radially outwardly for mixing together and reducing overall noise. However, the lobed mixer substantially increases engine weight and introduces aerodynamic friction and boattail drag which are undesirable, and is also relatively expensive.
Various forms of discrete tabs are also known for locally disrupting exhaust flow for effecting mixing thereof for reducing noise. However, a considerable problem associated with tabs is the associated drag and pressure losses therewith which decrease aerodynamic efficiency of the nozzle notwithstanding noise attenuation therefrom.
Accordingly, it is desired to provide an exhaust nozzle having improved noise attenuation capability with minimum reduction of aerodynamic efficiency.
A gas turbine engine exhaust nozzle includes an outlet for discharging exhaust, and a plurality of circumferentially spaced apart stub airfoils disposed adjacent the outlet. The airfoils shed vortices for mixing exhaust flow and attenuating noise with minimum thrust loss.